1. Field of the Invention
The present invention pertains to wireless telecommunications, and particularly to power control for transmitting over a downlink shared (e.g., common) chananel in a radio access network of a wireless (e.g., cellular) telecommunications system.
2. Related Art and other Considerations
In a typical cellular radio system, mobile user equipment units (UEs) communicate via a radio access network (RAN) to one or more core networks. The user equipment units (UEs) can be mobile stations such as mobile telephones (“cellular” telephones) and laptops with mobile termination, and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by a unique identity, which is broadcast in the cell. The base stations communicate over the air interface (e.g., radio frequencies) with the user equipment units (UE) within range of the base stations. In the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
One example of a radio access network is the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN). The UTRAN is a third generation system which in some respects builds upon the radio access technology known as Global System for Mobile communications (GSM) developed in Europe. UTRAN is essentially a wideband code division multiple access (W-CDMA) system.
As those skilled in the art appreciate, in W-CDMA technology a common frequency band allows simultaneous communication between a user equipment unit (UE) and plural base stations. Signals occupying the common frequency band are discriminated at the receiving station through spread spectrum CDMA waveform properties based on the use of a high speed, pseudo-noise (PN) code. These high speed PN codes are used to modulate signals transmitted from the base stations and the user equipment units (UEs). Transmitter stations using different PN codes (or a PN code offset in time) produce signals that can be separately demodulated at a receiving station. The high speed PN modulation also allows the receiving station to advantageously generate a received signal from a single transmitting station by combining several distinct propagation paths of the transmitted signal. In CDMA, therefore, a user equipment unit (UE) need not switch frequency when handoff of a connection is made from one cell to another. As a result, a destination cell can support a connection to a user equipment unit (UE) at the same time the origination cell continues to service the connection. Since the user equipment unit (UE) is always communicating through at least one cell during handover, there is no disruption to the call. Hence, the term “soft handover.” In contrast to hard handover, soft handover is a “make-before-break” switching operation.
The Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN) accommodates both circuit switched and packet switched connections. In this regard, in UTRAN the circuit switched connections involve a radio network controller (RNC) communicating with a mobile switching center (MSC), which in turn is connected to a connection-oriented, external core network, which may be (for example) the Public Switched Telephone Network (PSTN) and/or the Integrated Services Digital Network (ISDN). On the other hand, in UTRAN the packet switched connections involve the radio network controller communicating with a Serving GPRS Support Node (SGSN) which in turn is connected through a backbone network and a Gateway GPRS support node (GGSN) to packet-switched networks (e.g., the Internet, X.25 external networks)
There are several interfaces of interest in the UTRAN. The interface between the radio network controllers (RNCs) and the core network(s) is termed the “Iu” interface. The interface between a radio network controller (RNC) and its base stations (BSs) is termed the “Iub” interface. The interface between the user equipment unit (UE) and the base stations is known as the “air interface” or the “radio interface” or “Uu interface”. In some instances, a connection involves both a Serving or Source RNC (SRNC) and a target or drift RNC (DRNC), with the SRNC controlling the connection but with one or more diversity legs of the connection being handling by the DRNC. An Inter-RNC transport link can be utilized for the transport of control and data signals between Source RNC and a Drift or Target RNC, and can be either a direct link or a logical link as described, for example, in International Application Number PCT/US94/12419 (International Publication Number WO 95/15665). An interface between radio network controllers (e.g., between a Serving RNC [SRNC] and a Drift RNC [DRNC]) is termed the “Iur” interface.
The radio network controller (RNC) controls the UTRAN. In fulfilling its control role, the RNC manages resources of the UTRAN. Such resources managed by the RNC include (among others) the downlink (DL) power transmitted by the base stations; the uplink (UL) interference perceived by the base stations; and the hardware situated at the base stations.
Those skilled in the art appreciate that, with respect to a certain RAN-UE connection, an RNC can either have the role of a serving RNC (SRNC) or the role of a drift RNC (DRNC). If an RNC is a serving RNC (SRNC), the RNC is in charge of the connection with the user equipment unit (UE), e.g., it has full control of the connection within the radio access network (RAN). A serving RNC (SRNC) is connected to the core network. On the other hand, if an RNC is a drift RNC (DRNC), its supports the serving RNC (SRNC) by supplying radio resources (within the cells controlled by the drift RNC (DRNC)) needed for a connection with the user equipment unit (UE). A system which includes the drift radio network controller (DRNC) and the base stations controlled over the Iub Interface by the drift radio network controller (DRNC) is herein referenced as a DRNC system or DRNS.
On the radio interface, two groups of physical channels are defined: Dedicated physical channels and Common/Shared physical channels. Dedicated physical channels are used for transporting information between one user equipment unit (UE) and the core node (CN). In other words, the physical channels are dedicated to a certain user equipment unit (UE). Common/shared physical channels, on the other hand, can be used by multiple user equipment units (UEs) based on some kind of multiplexing. Multiplexing technologies used include both code and time division multiplexing.
The dedicated physical channel is further divided into the dedicated physical data channel (DPDCH) and the dedicated physical control channel (DPCCH). The former carries the user data and the latter carries control information related to the radio connection, e.g. information on what data rate is currently used etc. For more details on the physical channels see one or more of the following specifications (all of which are incorporated herein by reference in their entirety): (1) Third Generation Partnership Project (3GPP) Technical Specification 25.211, v.3.5.0 “Physical Channels and Mapping of Transport Channels Onto Physical Channels (FDD)”; (2) Third Generation Partnership Project (3GPP) Technical Specification 25.221, v.3.5.0 “Physical Channels and Mapping of Transport Channels Onto Physical Channels (TDD).”
In many radio access network (RAN) technologies, e.g. GSM, the user equipment unit (UE) will at any moment in time normally only exchange information with one RAN cell. This corresponds to having one radio link over the radio interface. When the user equipment unit (UE) moves from a first cell to a second cell in such a radio access network, the user equipment unit (UE) switches from the first cell to the second cell in an operation referred to as a “hard handover”.
However in other RAN technologies (e.g. WCDMA) it is possible for the user equipment unit (UE) to have information exchanged with several RAN cells. In such a RAN, when a UE is in an area where both the first cell and the second cell have coverage, the UE can have radio links to both the first cell and the second cell during a longer period. Both radio links will normally transport the same information and the UE (downlink) or RAN (uplink) can combine the information received over the different radio links in the best possible way. As noted above, the situation of having multiple radio links to one UE is often called “soft handover”.
The UTRAN supports a soft handover situation for dedicated physical channels only. As a result, if a UE is receiving both dedicated and shared physical channels, it can receive the dedicated channels from multiple UTRAN cells in parallel, whereas it will receive the shared channel information only via one UTRAN cell.
If a DRNC is providing resources for a UE-CN connection, there is a large difference in DRNC control for the two types of physical channels. For dedicated physical channels, the DRNC is involved in admission control at establishment of the UE-CN connection via its DRNS resources. When the DRNC has admitted the UE-CN connection to use its resources, the DRNC is no longer directly involved in the scheduling of the physical channel resources for the UE-CN connection. This task is performed by the SRNC. The DRNC might inform the SRNC about local conditions like a congestion situation and e.g. ask the SRNC to lower the information rate on the dedicated physical channel.
For common/shared physical channels, the DRNC is involved in admission control at establishment of the UE-CN connection via its DRNS resources. In addition, since this is a common/shared physical channel used by multiple UEs using this base station, the DRNC is continuously performing the final scheduling of the resources on the physical channel.
In the downlink direction from the radio access network (RAN) to the user equipment unit (UE), due to the scheduling in the DRNC, the UE will normally not know which common/shared physical channel resources will be used by the RAN for its UE-CN connection at each moment in time. In order to overcome this uncertainty, the UE can either listen to all common/shared physical channel resources and detect which resources are used for its UE-CN connection, or the RAN can inform the UE about the common/shared resources used at a certain point in time.
In line with the second solution, the RAN supports a method in which the UE is informed about the common/shared physical channel resources, e.g. the DSCH, used at a certain moment in time on a parallel established dedicated physical channel.
In the Universal Mobile Telecommunications (UMTS) Terrestrial Radio Access Network (UTRAN), on the radio interface there are Common Transport Channels and Dedicated Transport Channels. The Common Transport Channels are the uplink Random Access Channel (RACH), the downlink Forward Access Channel (FACH), uplink Common Packet Channel (CPCH), Uplink Shared Channel (USCH), and Downlink Shared Channel (DSCH). The Dedicated Transport Channels are the Dedicated Channel (DCH). The transport channels in the UMTS are described in one or more of the following specifications (all of which are incorporated herein by reference in their entirety): (1) Third Generation Partnership Project (3GPP) Technical Specification 25.211, v.3.5.0 “Physical Channels and Mapping of Transport Channels Onto Physical Channels (FDD)”; (2) Third Generation Partnership Project (3GPP) Technical Specification 25.221, v.3.5.0 “Physical Channels and Mapping of Transport Channels Onto Physical Channels (TDD)”; (3) Third Generation Partnership Project (3GPP) Technical Specification 25.331, v.3.5.0 “RRC Protocol Specification.”
The common transport channel (DSCH) is used for transporting data to many different UEs. The multiplexing is achieved by informing the UE about the DSCH resources, used at each moment in time for transmissions towards this UE, on the established dedicated physical channel in parallel with the DSCH.
The CRNC (assuming the role as DRNC for a UE) schedules the data received from the SRNC for the different UBs on the DSCH transport channel. When scheduling the DSCN data transmission the CRNC decides the power level to be used for each DSCH data sent towards the UE. This power level is indicated to the base station in the user plane frame protocol between the CRNC and the base station. In the Release '99 specifications the CRNC indicates an offset towards the power level of the Primary CPICH-. The power level of the Primary CPICH is fixed and known by both the CRNC and the BS (decided by the CRNC when configuring a cell). For more details on the user plane frame protocol between the CRNC and the base station used for the DSCH see Third Generation Partnership Project (3GPP) Technical Specification 25.435, v.3.5.0 “UThAN lub Interface User Plane Protocols for Common Transport Channel Data Streams.”
Site Selection Diversity Transmit power control (SSDT) is a scheme whereby a user equipment unit (UE) in soft handover can inform the cells (base stations) that it is connected to, which one of them is regarded as the primary (best) cell and consequently that the other cells that it is connected to are the secondary cells (non-primary). This scheme is defined such that normally a base station transmits both the DPDCH and the DPCCH in the downlink. However, for non-primary, cells the network may reduce (or switch off) the power in the downlink such that only the DPCCH is transmitted.
In the 3GPP specifications for Release '99 the power of the DSCH is set by the RNC scheduling the DSCH data, i.e. the CRNC. However, the CRNC does not have any information on whether or not the cell carrying the DSCH is the primary or a non-primary cell.
In the 3GPP Release 4 it is proposed to improve this power control such that the network may use SSDT information to decide the final power level of the DSCH. This would result in a possibility to have a lower power level if the cell carrying the DSCH is the primary cell and a higher power level if the cell carrying the DSCH is a non-primary cell. Note that the DSCH is not used in soft handover, but will always only be present on one radio link.
The current proposal discussed in 3GPP RAN3 for the network control is that the CRNC provides the base station with a power offset (PDSCH-secondary) to be used if the cell is a non-primary cell. This means that if the power level indicated in the user plane frame protocol is PDSCH then the following power levels would apply:
The DSCH is carried by the primary cell: PDSCH 
The DSCH is carried by a non-primary cell: PDSCH+PDSCH-secondary 
The mechanism proposed in 3GPP is to signal the power offset (PDSCH-secondary) to be used if the cell is a non-primary cell (PDSCH-secondary) from the CRNC to the base station when establishing a DSCH.
Since the CRNC does not know whether or not the base station supports the improved DSCH power control scheme (based on this additional offset) the support for this feature has to be signalled back to the CRNC. If the base station informs the CRNC that it is capable of this new feature then the CRNC shall set the power level in the scheduled data in the user plane such that the resulting power is PDSCH. If, on the other hand, the base station informs the CRNC that it does not support this new feature then the CRNC shall set the power level in the scheduled data in the user plane such that the resulting power is PDSCH+PDSCH-secondary. This to ensure a sufficient power level if the DSCH happens to be carried by a non-primary cell.
The solution currently proposed for 3GPP Release 4 has the drawback that the control of the mechanism becomes unnecessarily complex. The CRNC needs to wait for information on whether or not the base station supports the new power control scheme for the DSCH before it can decide what power level to set on the DSCH (in the user plane).
What is needed, therefore, and an object of the present invention, is a simplified power control scheme for the DSCH.